1. Field of the Invention
The present invention relates to well bore drilling techniques and completion methods for use in formations that present well bore stability and/or sand production problems either during the drilling operation and/or after well completion. Poorly consolidated sandstone or carbonate formations, coals, shales, or any formation that is highly stressed or that is reactive to the drilling fluid used would be included in these categories. Additionally, completion methods presented in this invention apply to methods used in completing such wells (whether vertical, horizontal, or inclined well bores) that effectively communicate the well bore with the targeted formation using various techniques including, but not limited to, hydraulic fracturing, oriented or nonoriented perforating, and hydrajetting of holes or slots.
2. Description of the Prior Art
The drilling of well bores in many formations is made more difficult by problems of formation instability. This can be caused by the presence of unusual or high stress within the formation, very low formation strength, or adverse reactions with drilling fluids. Further, the migration of formation particles with fluids produced from soft or poorly consolidated formations has also been a continuous problem. Numerous techniques have been developed to assist in controlling sand production including placing screens and/or gravel packs between the producing formations and the well bores penetrating them, utilizing hardenable resin coated particulate material to form consolidated gravel packs, or contacting the near well portions of poorly consolidated formations with consolidating fluids which subsequently harden. In many wells using these current methods sand production problems have continued. Sand production usually results in lost hydrocarbon production (or injectivity) due to the plugging of gravel packs, screens and perforations as well as production equipment such as flow lines, separators and the like. In some cases the result has been partial or complete well bore collapse, resulting in expensive workover or redrill operations.
When a formation is penetrated by a well bore, the near well bore material making up the formation must support the stress that was previously supported by the removed formation material. In a poorly consolidated rock formation, this stress may overcome the formation strength, causing the formation to breakdown and collapse into the well bore. This can cause loss of communication between the well bore tubular conduits and the remainder of the well bore beyond where such a collapse occurs. Additionally, if there is a high or otherwise unusual stress component in the formation, removal of formation material by the drilling process can cause a localized intensification of the stress field and also cause well bore collapse.
In a weak or poorly consolidated rock formation, this stress overcomes the formation strength which causes the formation to breakdown and sand to migrate into the well bore with produced fluids. As the poorly consolidated formation is produced over time, the breakdown of the formation progresses throughout the reservoir and the production of sand continues.
Thus, there is a need for improved methods of drilling and/or completing a well bore in certain formations and especially in poorly consolidated or highly stressed subterranean formations where well bores may be unstable or where stress induced formation failures during production may bring about sand production or well bore collapse.